This invention relates generally to thin film semiconductor X-Ray imaging arrays, and more particularly, to fabricating such an imaging array with a reduced data line resistance while simultaneously providing a thin film transistor (TFT) light blocking element.
Indirect thin film semiconductor imaging arrays typically include a photosensor array coupled to a scintillating medium. Radiation absorbed in the scintillator generates optical photons which in turn pass into a photosensor, such as a photodiode. The optical photon is absorbed in the photosensor and an electrical charge corresponding to an incident photon flux is generated. Substantially hydrogenated amorphous silicon (xcex1-Si) is commonly used in the fabrication of photosensors due to the advantageous photoelectric characteristics of xcex1-Si and the relative ease of fabricating such devices, especially for large area format devices. In particular, photosensitive elements, such as photodiodes, can be formed in connection with necessary control or switching elements, such as bottom-gated thin film transistors (TFTs), in a relatively large array. Radiation detectors and display arrays are typically fabricated on a large substrate on which many components, including TFTs, address lines, capacitors, and photosensors are formed through the sequential deposition and patterning of layers of conductive, semiconductive, and insulative materials.
At least one known fabrication process for such an X-Ray imaging array typically includes fabricating the TFT and then the photodiode. Fabricating a typical bottom-gated TFT includes the deposition and patterning of a metal layer to form the gate electrodes. A gate dielectric layer is then deposited over the gate electrode followed by the deposition and patterning of a layer of semiconductive material (typically, xcex1-Si). Various address lines are subsequently formed as the source/drain (data line) electrode layer is deposited, and patterned. The TFT array is then coated with a dielectric passivation layer prior to the fabrication of the photodiode active matrix. This dielectric layer is subsequently patterned to form contact windows to the underlying source/drain metallization. An xcex1-Si photodiode layer is then deposited and patterned to form the pixilated photosensor array. At this point, an additional dielectric passivation layer is deposited and patterned with a plurality of vias to provide interconnection to the TFT, diode, and other device elements. A final layer of metallization is deposited and etched to provide the appropriate electrical interconnection to the underlying device elements.
Overall system performance is improved as the system noise is decreased. The data line noise contribution to overall system noise is proportional to the square root of the data line series resistance. Thus, improved detector performance can be achieved by minimizing the electrical series resistance of the individual array data lines.
Illumination of the TFT by X-ray generated optical photons from the scintillator layer can induce OEFL (Optically Enhanced TFT Leakage). As the TFT leakage increases, the behavior of the associated pixel becomes non-linear and an erroneous signal is generated on other pixels connected to the same dataline which results in the formation of image artifacts. High levels of OEFL can therefore degrade overall detector performance.
In one known array formation process, several additional deposition and patterning steps, compared to the process described above in [0003], are required to achieve a reduction in data line series resistance and to form a light blocking shield over the TFT region. Each deposition and patterning step, involving photomasking and etching, increases detector fabrication costs as well as the likelihood of detector yield loss due to inadvertent damage to the active matrix array.
In one aspect, a method for fabricating a radiation detector including at least one Thin Film Transistor (TFT) is provided. The method includes forming a low resistance data line strap unitary with a light block element on the TFT.
In another aspect, a method for fabricating a radiation detector is provided. The method includes providing a thin film transistor (TFT), depositing a dielectric layer on the TFT, forming an opening for a data line strap via in the dielectric layer, and forming the data line strap via in the opening such that a data line strap is electrically coupled to a data line and the data line strap is unitary with a light block element.
In another aspect a radiation detector is provided. The radiation detector includes a thin film transistor (TFT) and a data line strap unitary with a light block element on the TFT.
In another aspect, a radiation detector is provided. The radiation detector includes a thin film transistor (TFT), a dielectric layer deposited on the TFT, an opening for a data line strap via in the dielectric layer, and a data line strap via in the opening such that the data line strap is electrically coupled to a data line and such that the data line strap is unitary with a light block element on the TFT.